Just to make it clear for anybody else, the exact code I used is this:
add_filter( 'generate_mobile_header_logo_output', function( $output ) {
if ( ! function_exists( 'generate_menu_plus_get_defaults' ) ) {
return $output;
}
$settings = wp_parse_args(
get_option( 'generate_menu_plus_settings', array() ),
generate_menu_plus_get_defaults()
);
return sprintf(
'<div class="site-logo mobile-header-logo">
<a href="%1$s" title="%2$s" rel="home">
<img src="%3$s" data-pin-nopin="1" width="999" height="999" alt="%4$s" />
</a>
</div>',
esc_url( apply_filters( 'generate_logo_href' , home_url( '/' ) ) ),
esc_attr( apply_filters( 'generate_logo_title', get_bloginfo( 'name', 'display' ) ) ),
esc_url( apply_filters( 'generate_mobile_header_logo', $settings['mobile_header_logo'] ) ),
esc_attr( apply_filters( 'generate_logo_title', get_bloginfo( 'name', 'display' ) ) )
);
} );